The present invention relates to a method for reading an image using a line image sensor, and an apparatus for reading an image a, such as a scanner or a facsimile device.
In reading an image using a line image sensor, reading has conventionally been carried out at the same space frequency in both the main scanning direction and the sub-scanning direction. FIG. 1 shows a row of pixels 63 of a line image sensor 62 within a CCD chip 61. There are pixels 63 with a vertical dimension and horizontal dimension that are both X, arranged the pixel pitch X. By causing the line image sensor 62 to scan in the main scanning direction (indicated by the arrow A) parallel to the lengthwise direction of the line image sensor 62 and, in addition, feeding a sheet of paper with an image drawn thereon in the sub-scanning direction (indicated by the arrow B) perpendicular to the main scanning direction, two-dimensional optical image information is read and converted into electric signals.
Supposing now that the dimension X of the pixels 63 is 125 .mu.m, for example, the reading in the main scanning direction is performed with the distance 1 mm divided for 8 pixels. Thus, inevitably, the reading accuracy in the main scanning direction is limited by the pixel pitch X.
Since the reading in the sub-scanning direction is carried out at the same spatial frequency as that at which the reading in the main scanning direction is carried out, this reading is also carried out with 1 mm in the vertical direction being divided for 8 pixels. In FIG. 2A, there is shown an image 64 with the height 1 mm to be read. In reading this image 64, it is necessary to move the line image sensor 62 in the sub-scanning direction, as shown in FIG. 2B. Actually, sub-scanning is performed by feeding a sheet of paper with the image 64 drawn thereon in the direction B, relative to the line image sensor 62 fixed in place. Thereby, the image 64 with the height 1 mm is read by the line image sensor 62 with the height 125 .mu.m, through 8 scannings from the first reading (R1) to the eighth reading (R8), having the image 64 of the height 1 mm divided by eight
Thus, the reading accuracy in the sub-scanning direction has also been affected by the pixel pitch X, so that it has been impossible to improve reading accuracy. Accuracy may be improved, however, if the pixel pitch X is made smaller, but this is restricted by the complexity of the fabrication process and increased cost.